The present invention relates to apparatus and techniques for performing minimally invasive surgery and, in particular to a retractor device for minimally invasive surgery.
Minimally invasive surgical techniques are becoming increasingly widespread in many different surgical fields. An area in which such techniques would appear to be particularly relevant is neurosurgical removal of Space-Occupying lesions (SOL), Intra Cerebral Hemorrhages (ICH), Intra Ventricular Hemorrhages (IVH), Intra Axial Brain Tumors (IABT), Intra Ventricular Brain Tumors (IVBT), and Other Brain lesions (OBL) and Brain Pathological Conditions (BPC).
In accordance with current methods, following initial imaging for locating a brain lesion, die skull is trepanned so as to remove a bone flap exposing an opening in the skull surface, an opening of from 1 cm×1 cm tip to 5 cm×5 cm, after which retractors are inserted into the brain tissue or lobes, and used to move and draw back brain tissue or lobs in the region of the lesion, thereby exposing the brain tissue for removal.
In cases in which the region of the lesion to be removed cannot be reached, a retractor is inserted into the brain tissue and is opened slowly in order to create a channel in the brain tissue enabling access to the lesion.
After a procedure which can take many hours, the retractor is removed and the bone flap is replaced 2D or 3D Ultrasound Imaging (USI) is performed once again so as to ensure that the entire lesion has, in fact, been removed.
Existing brain retractors allow only one dimensional retraction of the brain tissue, elevating Brain Retraction Pressure (BRP) to more than 20 mg Hg causing post-operation brain edema, or severe scarring. Known current neurosurgical intervention may cause the following complications:
a. infarction of brain tissue due to the localized pressure to which the retracted portions of the brain are subjected;
b. bleeding upon insertion of the retractors;
c. if several retractors need to be inserted, the pressure on the brain tissue is uneven, the lesion may not be properly exposed, possibly leading to a need to perform supplementary surgery in order to remove any remaining tumor tissue; or
d. insertion of the retractors and separation of the brain lobes are performed manually; these motions are thus inherently uneven, and are liable to cause trauma to the brain tissue.
Procedures are very lengthy and a number of surgical procedures are not carried at all out due to risk factors, or cannot be carried out successfully using current techniques. These include among others treating hemorrhage in the 4th ventricle or lateral ventricle, treating intra-ventricular hemorrhage, simultaneous removal of multiple metastases, direct treatment of brain abscess, and directly applied chemotherapy or radiotherapy of pathological tissue.
Edema caused by use of the retractor entails an increase in Intracranial Pressure (ICP), affecting the value of Cerebral Perfusion Pressure (CPP), which also depends on Mean Blood Pressure (MBP), according to the following association:CPP=MBP−ICP
The CPP must be within the range of 50-120 mm Hg. Increased dislocation and pressure on the brainstem could cause cessation of breathing and death of the patient.
The evolution of means of opening working channels includes the following generations: The first generation used a manually opened retractor, which was also held open manually. This type of retractor also generally included two arms which open and move away from each other in linear motion. This method has several main disadvantages, including the opening applying uneven pressure on brain tissue, the retractor's force is exerted only in the single direction or single dimensional of the linear opening. Furthermore, the retractor, which is hand-held by the human operator, is insufficiently stable, and any slight tremor of the operator's hands could damage brain tissue.
The second generation used the Yasargil retractor, which is the most common means used at present.
Prof. Yasargil (now living and working in the USA) is a Turkish medical scientist and neurosurgeon. He is the inventor of the Yasargil retractor, a self-retaining brain retractor, which avoids the need for manual holding of the brain retractor.
FIG. 1 of the prior art illustrates a Yasargil retractor 10. As shown in this illustration, the head of the patient 100 is on the operation table 13, to which retractor holder 14 is attached, also including arms 12 holding a pair of spatulas 11 which are inserted in to the head when they are both close to each other and are slowly distanced from each other to enlarge the canal which was created in order to enable a view of the Space Occupation Lesion (SOL) designated for treatment, and performing the treatment itself.
In spite of the significant improvement that this means provides over the previous generation, it still does not provide sufficient uniformity of the pressure applied on the brain tissue.
The third generation is the present inventor's First Radial Expansible Retractor (FRER) for minimally invasive surgery, described in PCT/IL00/00387, filed Jul. 4, 2000, which has significant improvements which can benefit patients.
FIG. 2a of the prior art illustrates side view of a FRER 300. FRER 300 includes a FRER planar base 21, a FRER upper plate 22, a FRER lower plate 23 having a FRER central opening 25, FRER linear drive elements 24, FRER longitudinal ribs 26 comprising a FRER expansible needle shaped retractor 27, which are parallel to FRER axis 29 which is perpendicular to FRER planar base 21, and a FRER probe 28.
FIG. 2b of the prior art is a lateral cross-section view of the FRER 300 of FIG. 2a, showing the FRER expansion mechanism 31 which serves to generate the opening and closing motions of the FRER expansible needle shaped retractor, also including the FRER linear drive elements 24 and FRER outer cogwheel 32, and FRER inward facing pluralities of teeth 33 and the FRER longitudinal ribs 26.
It is of utmost importance for the retractor's opening rate to be controlled and the mechanism controlling the opening rate must be able to allow a nonlinear opening rate. Initially, the brain's resistance to the opening retractor is relatively small, and increases at a linear rate as the opening increases. A suitable opening rate at this stage is approximately 10 microns per second. Once the opening has reached a diameter of approximately 20 to 30 mm, the brain's resistance is no longer linear, and the larger the diameter, the faster the resistance increases, therefore, at this stage the opening rate must be slower, within a range of 3 to 5 microns per second, in order to prevent damage to brain tissue. Achieving such a change of rate in an opening mechanism based on cogwheels is possible only by means of changing the manual rotation rate of the external rotating wheel.
In addition, an entirely different method was demonstrated in the Cincinnati Children's Hospital Medical Center in Ohio by Dr. Crone, in which a sausage-like balloon was inserted into the brain, was gradually inflated mid kept in the brain for several days. The balloon was inflated slowly, spreading and creating a safe pathway, afterwards the inflation was ceased and the balloon was removed from the brain, leaving a gap in the brain which could be used as a working channel.
This method requires anesthetizing the patient more than once, thus increasing the risk to his life.
There is thus a widely recognized need for, and it would be highly advantageous to have, a radial expansible retractor for minimally invasive surgery which enables opening a channel while exerting force on the surrounding tissue as uniformly as possible when inserted into brain tissue, while achieving a continuous opening rate and value suitable for the respective CPP at every stage of the opening.